Investigation into the feasibility of cyclone with underflow and bypass flow for improving the performance of circulating fluidized beds

The cyclone is one of the important components of the circulating fluidized bed (CFB). In this paper, the cyclone with underflow and bypass flow (CUB) is applied to the circulating fluidized bed to improve its combustion efficiency. The turbulence within the CUB was calculated using a Reynolds stress model and a mixture model, while the short-circuit flow was traced. The trajectory of particulate matter was determined through discrete phase model. The combustion process of the CFB is simulated by using the Computational Particle Fluid Dynamics (CPFD) method. The simulation results demonstrate that the CUB exhibits highest separation efficiency for 10 μm and 2.5 μm particulate matter, achieving approximately 97 % and 86 %, respectively, when the sleeve length is set at 24 mm and there is no vortex finder present. The configuration of the CUB enhances the recycling rate of fine fuel and improves the combustion efficiency. The carbon content fraction of the particles also decreased from about 0.7 to about 0.4 which led to a reduction in the density of the emitted particulate matter. In addition, after being equipped with the CUB, the particle size range of the fuel and desulfurizer can be adjusted, optimizing the aerodynamic characteristics of the combustion chamber, the combustion efficiency of the fuel, and the desulfurization efficiency of the desulfurizer.